Systems and methods for treatments of an eye with a photosensitizer

ABSTRACT

A formulation for an eye treatment includes a photosensitizer and a permeability enhancing composition. The permeability enhancing composition includes one or more permeability enhancers. The permeability enhancing composition has a hydrophilic and lipophilic balance increases a permeability of an area of the eye for the photosensitizer. The hydrophilic and lipophilic balance can be characterized by a Hydrophile-Lipophile Balance (HLB) number. For example, the area of the eye may include a corneal epithelium, the photosensitizer may include riboflavin, and the permeability enhancing composition may have a corresponding HLB number between approximately 12.6 and approximately 14.6.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 62/195,144, filed Jul. 21, 2015, U.S. Provisional Patent Application No. 62/255,452, filed Nov. 14, 2015, U.S. Provisional Patent Application No. 62/262,919, filed Dec. 4, 2015, and U.S. Provisional Patent Application No. 62/263,598, filed Dec. 4, 2015, the contents of these application being incorporated entirely herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure pertains to systems and methods for treating the eye, and more particularly, to systems and methods for delivering a photosensitizer to regions of the eye for eye treatments.

Description of Related Art

Certain photosensitizers may be applied to the eye for eye treatments. For example, photosensitizers can generate cross-linking activity in the cornea. Cross-linking can treat disorders, such as keratoconus. In particular, keratoconus is a degenerative disorder of the eye in which structural changes within the cornea cause it to weaken and change to an abnormal conical shape. Cross-linking treatments can strengthen and stabilize areas weakened by keratoconus and prevent undesired shape changes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example system that delivers a cross-linking agent and photoactivating light to a cornea of an eye in order to generate cross-linking of corneal collagen, according to aspects of the present disclosure.

FIGS. 2A-B illustrate a diagram for photochemical kinetic reactions involving riboflavin and photoactivating light (e.g., ultraviolet A (UVA) light) applied during a corneal cross-linking treatment, according to aspects of the present disclosure.

FIGS. 3A-C illustrate graphs showing the correlation between model values and experimental data for oxygen depletion experiments, where the model values are based on a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIG. 4 illustrates a graph showing the correlation between model values and experimental data for non-linear optical microscopy fluorescence experiments, where the model values are based on a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIGS. 5A-D illustrate graphs showing the correlation between model values and experimental data for fluorescence data based on papain digestion method experiments, where the model values are based on a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIGS. 6A-B illustrate graphs showing the correlation between model values and experimental data for conical stromal demarcation line experiments, where the model values are based on a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIGS. 7A-C illustrate graphs of cross-link profiles for treatments using different protocols, as generated by a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIGS. 8A-C illustrate graphs of cross-link profiles for treatments using different protocols, as generated by a model of photochemical kinetic reactions, where the cross-link profiles are evaluated to determine the depth for a demarcation line for each protocol according to aspects of the present disclosure.

FIGS. 9A-B illustrate graphs of demarcation depth versus dose of photoactivating light based on cross-link profiles for treatments using different protocols, as generated by a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIG. 10 illustrates a graph of cross-link profiles for treatments using different protocols as generated by a model of photochemical kinetic reactions, where the cross-link profiles are evaluated to determine the depth for a demarcation line for each protocol according to aspects of the present disclosure.

FIG. 11 illustrates the measurement of maximum keratometry (K_(max)) at six and twelve months relative to a baseline for corneas that were experimentally treated according to the protocols employed for FIG. 10.

FIG. 12A illustrates a graph that plots, for the biomechanical stiffness depth determined for each protocol in FIG. 10, the experimental change of K_(max) for months six and twelve corresponding to the respective protocol, according to aspects of the present disclosure.

FIG. 12B illustrates a graph that plots, for the area above the demarcation line for each protocol in FIG. 10, the experimental change of K_(max) for months six and twelve corresponding to the respective protocol, according to aspects of the present disclosure.

FIG. 13 illustrates an example system employing a model of photochemical kinetic reactions according to aspects of the present disclosure.

FIG. 14 illustrates relative diffusivity values for different formulations applied to corneas.

FIG. 15 illustrates relative fluorescence values for cross-linked corneas treated with different riboflavin formulations.

FIG. 16 illustrates different parameters for treating corneas with different riboflavin formulations.

FIG. 17 illustrates relative fluorescence values for cross-linked corneas treated according to the parameters in FIG. 16.

FIGS. 18-20 illustrate relative fluorescence for cross-linked corneal flaps treated with different surfactants in riboflavin solution.

FIG. 21 illustrates relative fluorescence for cross-linked corneal flaps treated with a riboflavin solution that does not include benzalkonium chloride (BAC), relative to a riboflavin solution that includes BAC as a permeability enhancer.

FIGS. 22-24 illustrate relative fluorescence for cross-linked corneal flaps treated with riboflavin solutions that include different concentrations of Polidocanol as a permeability enhancer, relative to other riboflavin solutions that include BAC as a permeability enhancer and to other riboflavin solutions without any permeability enhancer.

FIGS. 25-26 illustrate relative fluorescence for cross-linked corneal flaps treated with riboflavin solutions that include different concentrations of Polidocanol as a permeability enhancer or riboflavin solutions that include different concentrations of Polidocanol as well as Fe(II) as an additive, relative to other riboflavin solutions that include BAC as a permeability enhancer.

FIG. 27 illustrates relative fluorescence of cross-linked flaps treated with one of two different surfactants or a combination of the two surfactants.

FIG. 28A illustrates Brillouin modulus values measured at anterior, central, and posterior sections of corneas experimentally soaked in riboflavin for various durations and irradiated with UV light for various durations.

FIG. 28B illustrates the experimentally measured Brillouin modulus values and values calculated with a model of photochemical kinetic reactions for various cross-linking treatments.

FIG. 29 illustrates concentration of cross-link concentration as well as a function of conical depth with a demarcation depth as well as the second derivative.

FIG. 30 illustrates another graph of data showing the correlation of model values and experimental data for the depths of corneal stromal demarcation lines for protocols described in fourteen separate studies.

FIG. 31 illustrates a graph of cross-link profiles (cross-link concentration as a function of conical depth) calculated by a model of photochemical kinetic reactions for various cross-linking treatments in extensiometry experiments.

FIG. 32 illustrates a correlation of extensiometry measurements and values calculated by the model for the various cross-linking treatments in the experiments of FIG. 31.

FIG. 33 illustrates how by a model of photochemical kinetic reactions allows particular aspects of the photochemical process to be controlled or otherwise influenced to produce desired cross-linking activity.

FIG. 34 shows the effect of the various additives in FIG. 33 on cross-linking activity.

FIGS. 35-36 illustrate graphs of cross-link profiles for treatments employing different protocols as generated by a model of photochemical kinetic reactions.

FIG. 37 illustrates that the demarcation line depth may be affected by aspects of the riboflavin concentration, the use of thickening agent, illumination (UVA) device calibration, illumination (UVA) beam profile, and/or geographic factors.

FIG. 38 illustrates an example system employing a model of photochemical kinetic reactions to provide treatment parameters for achieving desired biomechanical changes according to aspects of the present disclosure.

FIG. 39 an example method employing a model of photochemical kinetic reactions to determine treatment parameters for achieving desired biomechanical changes according to aspects of the present disclosure.

SUMMARY

Aspects of the present disclosure relate to systems and methods for delivering a photosensitizer to regions of the eye for eye treatments. In particular, the systems and methods employ formulations that enhance the permeability of eye structures, such as the corneal epithelium, to facilitate delivery of photosensitizers to desired areas.

According to aspects of the present disclosure, a formulation for an eye treatment includes a photosensitizer and a permeability enhancing composition. The permeability enhancing composition includes one or more permeability enhancers. The permeability enhancing composition has a Hydrophile-Lipophile Balance (HLB) number indicating that the permeability enhancing composition increases a permeability of an area of the eye for the photosensitizer. In some cases, the permeability enhancing composition includes a plurality of permeability enhancers, where the HLB number for the permeability enhancing composition is equal to a sum of products multiplying a percentage of each permeability enhancer in the permeability enhancing composition and a HLB number for the respective permeability enhancer. In other cases, the formulation further includes at least one additive selected from the group consisting of iron, copper, manganese, chromium, vanadium, aluminum, cobalt, mercury, cadmium, nickel, arsenic, 2,3-butanedione, and folic acid. For example, the at least one additive includes iron(II). In further cases, the area of the eye is a corneal epithelium. In yet further cases, the photosensitizer includes riboflavin and the permeability enhancing composition has a HLB number between approximately 12.6 and approximately 14.6. In alternative cases, the area of the eye is an area infected by a pathogen.

According to further aspects of the present disclosure, a method for treating an eye includes applying the formulation above to an area of an eye and photoactivating the photosensitizer by delivering a dose of illumination to the area of the eye. In some cases, the method further includes applying a concentration of oxygen to the cornea. In other cases, applying the formulation includes applying the formulation to an area of the eye infected by a pathogen, whereby photoactivation of the photosensitizer provides an antimicrobial effect on the area infected by the pathogen. In alternative cases, applying the formulation includes applying the formulation to a corneal epithelium.

According to other aspects of the present disclosure, a formulation for a corneal treatment includes a photosensitizer and a non-ionic surfactant. The non-ionic surfactant includes a molecule having a hydrophilic and lipophilic balance that increases the permeability of the corneal epithelium for the photosensitizer. In some cases, the photosensitizer includes riboflavin and the non-ionic surfactant has a Hydrophile-Lipophile Balance (HLB) number between approximately 12.6 and approximately 14.6. In other cases, the non-ionic surfactant includes Polyoxyethylene (9) lauryl ether. In yet other cases, the formulation includes at least one additive including selected from the group consisting of iron, copper, manganese, chromium, vanadium, aluminum, cobalt, mercury, cadmium, nickel, arsenic, 2,3-butanedione, and folic acid. For example, the at least one additive includes iron(II).

DESCRIPTION

FIG. 1 illustrates an example treatment system 100 for generating cross-linking of collagen in a cornea 2 of an eye 1. The treatment system 100 includes an applicator 132 for applying a cross-linking agent 130 to the cornea 2. In example embodiments, the applicator 132 may be an eye dropper, syringe, or the like that applies the photosensitizer 130 as drops to the cornea 2. The cross-linking agent 130 may be provided in a formulation that allows the cross-linking agent 130 to pass through the corneal epithelium 2 a and to underlying regions in the corneal stroma 2 b. Alternatively, the corneal epithelium 2 a may be removed or otherwise incised to allow the cross-linking agent 130 to be applied more directly to the underlying tissue.

The treatment system 100 includes an illumination system with a light source 110 and optical elements 112 for directing light to the cornea 2. The light causes photoactivation of the cross-linking agent 130 to generate cross-linking activity in the cornea 2. For example, the cross-linking agent may include riboflavin and the photoactivating light may be ultraviolet A (UVA) (e.g., 365 nm) light. Alternatively, the photoactivating light may have another wavelength, such as a visible wavelength (e.g., 452 nm). As described further below, corneal cross-linking improves corneal strength by creating chemical bonds within the corneal tissue according to a system of photochemical kinetic reactions. For instance, riboflavin and the photoactivating light are applied to stabilize and/or strengthen corneal tissue to address diseases such as keratoconus or post-LASIK ectasia.

The treatment system 100 includes one or more controllers 120 that control aspects of the system 100, including the light source 110 and/or the optical elements 112. In an implementation, the cornea 2 can be more broadly treated with the cross-linking agent 130 (e.g., with an eye dropper, syringe, etc.), and the photoactivating light from the light source 110 can be selectively directed to regions of the treated cornea 2 according to a particular pattern.

The optical elements 112 may include one or more mirrors or lenses for directing and focusing the photoactivating light emitted by the light source 110 to a particular pattern on the cornea 2. The optical elements 112 may further include filters for partially blocking wavelengths of light emitted by the light source 110 and for selecting particular wavelengths of light to be directed to the cornea 2 for activating the cross-linking agent 130. In addition, the optical elements 112 may include one or more beam splitters for dividing a beam of light emitted by the light source 110, and may include one or more heat sinks for absorbing light emitted by the light source 110. The optical elements 112 may also accurately and precisely focus the photo-activating light to particular focal planes within the cornea 2, e.g., at a particular depths in the underlying region 2 b where cross-linking activity is desired.

Moreover, specific regimes of the photoactivating light can be modulated to achieve a desired degree of cross-linking in the selected regions of the cornea 2. The one or more controllers 120 may be used to control the operation of the light source 110 and/or the optical elements 112 to precisely deliver the photoactivating light according to any combination of: wavelength, bandwidth, intensity, power, location, depth of penetration, and/or duration of treatment (the duration of the exposure cycle, the dark cycle, and the ratio of the exposure cycle to the dark cycle duration).

The parameters for photoactivation of the cross-linking agent 130 can be adjusted, for example, to reduce the amount of time required to achieve the desired cross-linking. In an example implementation, the time can be reduced from minutes to seconds. While some configurations may apply the photoactivating light at an irradiance of 5 mW/cm², larger irradiance of the photoactivating light, e.g., multiples of 5 mW/cm², can be applied to reduce the time required to achieve the desired cross-linking. The total dose of energy absorbed in the cornea 2 can be described as an effective dose, which is an amount of energy absorbed through an area of the corneal epithelium 2 a. For example the effective dose for a region of the corneal surface 2A can be, for example, 5 J/cm², or as high as 20 J/cm² or 30 J/cm². The effective dose described can be delivered from a single application of energy, or from repeated applications of energy.

The optical elements 112 of the treatment system 100 may include a digital micro-mirror device (DMD) to modulate the application of photoactivating light spatially and temporally. Using DMD technology, the photoactivating light from the light source 110 is projected in a precise spatial pattern that is created by microscopically small mirrors laid out in a matrix on a semiconductor chip. Each mirror represents one or more pixels in the pattern of projected light. With the DMD one can perform topography guided cross-linking. The control of the DMD according to topography may employ several different spatial and temporal irradiance and dose profiles. These spatial and temporal dose profiles may be created using continuous wave illumination but may also be modulated via pulsed illumination by pulsing the illumination source under varying frequency and duty cycle regimes as described above. Alternatively, the DMD can modulate different frequencies and duty cycles on a pixel by pixel basis to give ultimate flexibility using continuous wave illumination. Or alternatively, both pulsed illumination and modulated DMD frequency and duty cycle combinations may be combined. This allows for specific amounts of spatially determined corneal cross-linking. This spatially determined cross-linking may be combined with dosimetry, interferometry, optical coherence tomography (OCT), corneal topography, etc., for pre-treatment planning and/or real-time monitoring and modulation of corneal cross-linking during treatment. Additionally, pre-clinical patient information may be combined with finite element biomechanical computer modeling to create patient specific pre-treatment plans.

To control aspects of the delivery of the photoactivating light, embodiments may also employ aspects of multiphoton excitation microscopy. In particular, rather than delivering a single photon of a particular wavelength to the cornea 2, the treatment system 100 may deliver multiple photons of longer wavelengths, i.e., lower energy, that combine to initiate the cross-linking. Advantageously, longer wavelengths are scattered within the cornea 2 to a lesser degree than shorter wavelengths, which allows longer wavelengths of light to penetrate the cornea 2 more efficiently than shorter wavelength light. Shielding effects of incident irradiation at deeper depths within the cornea are also reduced over conventional short wavelength illumination since the absorption of the light by the photosensitizer is much less at the longer wavelengths. This allows for enhanced control over depth specific cross-linking. For example, in some embodiments, two photons may be employed, where each photon carries approximately half the energy necessary to excite the molecules in the cross-linking agent 130 to generate the photochemical kinetic reactions described further below. When a cross-linking agent molecule simultaneously absorbs both photons, it absorbs enough energy to release reactive radicals in the corneal tissue. Embodiments may also utilize lower energy photons such that a cross-linking agent molecule must simultaneously absorb, for example, three, four, or five, photons to release a reactive radical. The probability of the near-simultaneous absorption of multiple photons is low, so a high flux of excitation photons may be required, and the high flux may be delivered through a femtosecond laser.

A large number of conditions and parameters affect the cross-linking of corneal collagen with the cross-linking agent 130. For example, when the cross-linking agent 130 is riboflavin and the photoactivating light is UVA light, the irradiance and the dose both affect the amount and the rate of cross-linking. The UVA light may be applied continuously (continuous wave (CW)) or as pulsed light, and this selection has an effect on the amount, the rate, and the extent of cross-linking.

If the UVA light is applied as pulsed light, the duration of the exposure cycle, the dark cycle, and the ratio of the exposure cycle to the dark cycle duration have an effect on the resulting corneal stiffening. Pulsed light illumination can be used to create greater or lesser stiffening of corneal tissue than may be achieved with continuous wave illumination for the same amount or dose of energy delivered. Light pulses of suitable length and frequency may be used to achieve more optimal chemical amplification. For pulsed light treatment, the on/off duty cycle may be between approximately 1000/1 to approximately 1/1000; the irradiance may be between approximately 1 mW/cm² to approximately 1000 mW/cm² average irradiance, and the pulse rate may be between approximately 0.01 HZ to approximately 1000 Hz or between approximately 1000 Hz to approximately 100,000 Hz.

The treatment system 100 may generate pulsed light by employing a DMD, electronically turning the light source 110 on and off, and/or using a mechanical or opto-electronic (e.g., Pockels cells) shutter or mechanical chopper or rotating aperture. Because of the pixel specific modulation capabilities of the DMD and the subsequent stiffness impartment based on the modulated frequency, duty cycle, irradiance and dose delivered to the cornea, complex biomechanical stiffness patterns may be imparted to the cornea to allow for various amounts of refractive correction. These refractive corrections, for example, may involve combinations of myopia, hyperopia, astigmatism, irregular astigmatism, presbyopia and complex corneal refractive surface corrections because of ophthalmic conditions such as keratoconus, pellucid marginal disease, post-lasik ectasia, and other conditions of corneal biomechanical alteration/degeneration, etc. A specific advantage of the DMD system and method is that it allows for randomized asynchronous pulsed topographic patterning, creating a non-periodic and uniformly appearing illumination which eliminates the possibility for triggering photosensitive epileptic seizures or flicker vertigo for pulsed frequencies between 2 Hz and 84 Hz.

Although example embodiments may employ stepwise on/off pulsed light functions, it is understood that other functions for applying light to the cornea may be employed to achieve similar effects. For example, light may be applied to the cornea according to a sinusoidal function, sawtooth function, or other complex functions or curves, or any combination of functions or curves. Indeed, it is understood that the function may be substantially stepwise where there may be more gradual transitions between on/off values. In addition, it is understood that irradiance does not have to decrease down to a value of zero during the off cycle, and may be above zero during the off cycle. Desired effects may be achieved by applying light to the cornea according to a curve varying irradiance between two or more values.

Examples of systems and methods for delivering photoactivating light are described, for example, in U.S. Patent Application Publication No. 2011/0237999, filed Mar. 18, 2011 and titled “Systems and Methods for Applying and Monitoring Eye Therapy,” U.S. Patent Application Publication No. 2012/0215155, filed Apr. 3, 2012 and titled “Systems and Methods for Applying and Monitoring Eye Therapy,” and U.S. Patent Application Publication No. 2013/0245536, filed Mar. 15, 2013 and titled “Systems and Methods for Corneal Cross-Linking with Pulsed Light,” the contents of these applications being incorporated entirely herein by reference.

The addition of oxygen also affects the amount of corneal stiffening. In human tissue, O₂ content is very low compared to the atmosphere. The rate of cross-linking in the cornea, however, is related to the concentration of O₂ when it is irradiated with photoactivating light. Therefore, it may be advantageous to increase or decrease the concentration of O₂ actively during irradiation to control the rate of cross-linking until a desired amount of cross-linking is achieved. Oxygen may be applied during the cross-linking treatments in a number of different ways. One approach involves supersaturating the riboflavin with O₂. Thus, when the riboflavin is applied to the eye, a higher concentration of O₂ is delivered directly into the cornea with the riboflavin and affects the reactions involving O₂ when the riboflavin is exposed to the photoactivating light. According to another approach, a steady state of O₂ (at a selected concentration) may be maintained at the surface of the cornea to expose the cornea to a selected amount of O₂ and cause O₂ to enter the cornea. As shown in FIG. 1, for instance, the treatment system 100 also includes an oxygen source 140 and an oxygen delivery device 142 that optionally delivers oxygen at a selected concentration to the cornea 2. Example systems and methods for applying oxygen during cross-linking treatments are described, for example, in U.S. Pat. No. 8,574,277, filed Oct. 21, 2010 and titled “Eye Therapy,” U.S. Patent Application Publication No. 2013/0060187, filed Oct. 31, 2012 and titled “Systems and Methods for Corneal Cross-Linking with Pulsed Light,” the contents of these applications being incorporated entirely herein by reference.

In general, the structure of the cornea includes five layers. From the outer surface of the eye inward, these are: (1) epithelium, (2) Bowman's layer, (3) stroma, (4) Descemet's membrane, and (5) endothelium. During example cross-linking treatments, the stroma is treated with riboflavin, a photosensitizer, and ultraviolet (UV) light is delivered to the cornea to activate the riboflavin in the stroma. Upon absorbing UV radiation, riboflavin undergoes a reaction with oxygen in which reactive oxygen species and other radicals are produced. These reactive oxygen species and other radicals further interact with the collagen fibrils to induce covalent bonds that bind together amino acids of the collagen fibrils, thereby cross-linking the fibrils. The photo-oxidative induction of collagen cross-linking enhances the biomechanical strength of the stroma, and can provide therapeutic benefits for certain ophthalmic conditions, such as keratoconus, or generate refractive changes to correct myopia, hyperopia and/or astigmatism.

As the outer-most barrier of the cornea, the epithelium functions to regulate nutrients, including oxygen, that are admitted into the stromal tissue from the tear film. This regulation is carried out via the epithelium's physiological “pumps” that are driven by osmotic pressure across the epithelium due to differential concentrations of barrier-permeable solutes on either side of the epithelium. When healthy, certain nutrients in the tear film that become depleted within the stroma can permeate the epithelium via osmotic pressure to resupply the stroma. However, while oxygen and some other small molecule nutrients can reach the stroma according to this mechanism, certain photosensitizers cannot pass through the epithelium.

Riboflavin, for example, is a relatively large, hydrophilic molecule that cannot penetrate the tight junctions of the epithelium. The epithelium slows the amount of riboflavin that can penetrate the stroma. Thus, a variety of approaches have been employed to overcome low riboflavin diffusivity and deliver sufficient concentrations of riboflavin to the stroma for performing corneal cross-linking treatments. According to one approach, the epithelium is removed (epithelium debridement) before a riboflavin solution is applied directly to the stroma. Although removing the epithelium allows riboflavin to reach the stroma, the approach is associated with patient discomfort, risks of infection, and other possible complications.

Meanwhile, other approaches avoid epithelial debridement. For example, riboflavin may be provided in a formulation that allows the cross-linking agent to pass through the epithelium. Such formulations are described, for example, in U.S Patent Application Publication No. 2010/0286156, filed on May 6, 2009 and titled “Collyrium for the Treatment of Conical Cornea with Cross-Linking Trans-Epithelial Technique, and in U.S. Patent Application Publication No. 2013/0267528, filed on Jan. 4, 2013 and titled “Trans-Epithelial Osmotic Collyrium for the Treatment of Keratoconus,” the contents of these applications being incorporated entirely herein by reference. In particular, some riboflavin formulations include ionic agents, such as benzalkonium chloride (BAC), with a specific osmolarity of sodium chloride (NaCl). Although such formulations may enhance permeability of the epithelium, they are disadvantageously corrosive to the epithelium.

Additionally or alternatively, another solution and/or mechanical forces may be applied to enhance the permeability of the epithelium and allow the riboflavin to pass more easily through the epithelium. Examples of approaches for enhancing or otherwise controlling the delivery of a cross-linking agent to the underlying regions of the cornea are described, for example, in U.S. Patent Application Publication No. 2011/0288466, filed Apr. 13, 2011 and titled “Systems and Methods for Activating Cross-Linking in an Eye,” and U.S. Patent Application Publication No. 2012/0289886, filed May 18, 2012 and titled “Controlled Application of Cross-Linking Agent,” the contents of these applications being incorporated entirely herein by reference.

The present disclosure teaches the use of another class of riboflavin formulations. Advantageously, such formulations enhance the permeability of the epithelium sufficiently to allow relatively large hydrophilic riboflavin molecules (or Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, molecules) to pass through the epithelium without debridement, but the permeability is not enhanced to a point where the epithelium becomes damaged. To enhance permeability, such formulations employ a non-ionic agent that is chosen using the Hydrophile-Lipophile Balance (HLB) system.

The HLB of a permeability enhancer indicates the balance of hydrophilic and lipophilic groups in the molecular structure of the enhancer. Permeability enhancers (or emulsifiers) for the epithelium include a molecule which has both hydrophilic and lipophilic groups. Molecules with HLB number below 9 are considered lipophilic and those above 11 as hydrophilic. Molecules with HLB number between 9 and 11 are intermediate.

For the corneal epithelium, a HLB number that is too great or too small does not help the passage of a photosensitizer through the epithelium. A specific HLB range enhances movement of a photosensitizer through the epithelium. Thus, aspects of the present disclosure employ non-ionic agents that have a hydrophilic/lipophilic balance to achieve optimized diffusivity through the epithelium and the stroma. Advantageously, non-ionic agents are also less corrosive and damaging to the epithelium than ionic agents, such as BAC.

For riboflavin, the HLB range for more effective permeability enhancers has been experimentally determined by the inventors to be between approximately 12.6 and approximately 14.6. A class of permeability enhancers includes various forms of polyethylene glycol (PEG) with different aliphatic chain lengths. According to example embodiments, some riboflavin formulations include specific concentrations of Polidocanol (Polyoxyethylene (9) lauryl ether), which has a HLB number of approximately 13.6.

To calculate the HLB for molecules or combinations of molecules where the hydrophilic portion consists of ethylene oxide only, the formula is:

HLB=E/5, where E=weight percentage oxyethylene content.

In general, the HLB range for enhancers that achieve more effective permeability may vary according to different aspects of the formulation. In particular, the HLB range for more optimal enhancers may vary according to the photosensitizer employed in the formulation. For instance, more optimal permeability might be achieved for other photosensitizers, such as Rose Bengal, by employing enhancers in a HLB range that is different from that for riboflavin (e.g., HLB of approximately 12.6 to approximately 14.6).

Furthermore, the formulation may include other additives that may affect the HLB range for more optimal enhancers. For instance, riboflavin formulations may also include iron ions, such as Fe(II). Additives that may be included in photosensitizer formulations are described, for example, in U.S. Patent Application Publication No. 2014/0343480, filed May 19, 2014 and titled “Systems, Methods, and Compositions for Cross-linking,” and U.S. Provisional Patent Application No. 62/086,572, filed Dec. 2, 2014 and titled “Systems, Methods, and Compositions for Cross-linking,” the contents of these applications being incorporated entirely herein by reference. Other additives, for instance, include copper, manganese, chromium, vanadium, aluminum, cobalt, mercury, cadmium, nickel, arsenic, 2,3-butanedione, and folic acid.

Additionally, several permeability enhancers may be combined to achieve a specific HLB that achieves more effective permeability for the epithelium. These may be calculated by taking the percentage of each enhancer, multiplying it by its HLB number, and then summing the results. For instance, in a formulation including 30% enhancer A with a HLB number of approximately 14, 50% enhancer B with a HLB number of approximately 6, and 20% enhancer C with a HLB number of approximately 14, the estimated HLB number can be calculated as:

30%×HLB 14 for A=4.2;

50%×HLB 6 for B=3.0;

20%×HLB 14 for C=2.8;

Estimated HLB number for combination of A+B+C=4.2+3.0+2.8=10.0

Thus, two or more enhancers may be combined to achieve a very specific HLB number, where a single enhancer may provide less optimal permeability. Additionally, combining different enhancers might offer other desirable properties of the final formulation with regard to solubility, viscosity, stability or some other desirable attribute.

Study 1

In a study, a Franz cell was employed to measure diffusivity of riboflavin formulations containing BAC or a non-ionic agent in porcine eyes with or without an epithelia of approximately 100 μm. FIG. 14 illustrates a graph of diffusivity values for the formulations in this study. Column A represents the application of a saline solution of 0.1% riboflavin to porcine eyes without epithelia (epi-off). Column B represents the application of a 0.22% riboflavin solution with BAC to porcine eyes epi-off. Column C represents the application of a 0.22% riboflavin solution with a non-ionic agent to porcine eyes with epithelia (epi-on). Column D represents the application of a 0.22% riboflavin solution with BAC to porcine eyes epi-on. Column E represents the application of a saline solution of 0.1% riboflavin to porcine eyes epi-on. The results indicates the formulation with the non-ionic agent formulation achieved faster diffusion than the ionic formulation with BAC. Furthermore, the diffusivity of the formulation with the non-ionic agent applied epi-on is similar to the diffusivity for the formulations applied epi-off. Thus, a sufficient hydrophilic/lipophilic balance was achieved with the non-ionic agent.

Study 2

In a study, porcine eyes shipped overnight on ice from an abattoir (SiouxPreme, Sioux City, Iowa) were cleaned and soaked for 20 minutes in an incubator set at 37° C. with a 0.22% riboflavin solution with BAC or a 0.22% riboflavin solution with a non-ionic agent. The corneas had epithelia of approximately 100 μm. The epithelia of the corneas were removed after the respective soaks and prior to pan-corneal irradiation with UVA light. The treatment protocol employed applying pulsed UVA light (1 second on; 1 second off) at an irradiation of 30 mW/cm² and for a dose of 7.2 J/cm², while the corneas were exposed to 100% concentration of oxygen gas. 200 μm corneal flaps were cut using a femtosecond laser. The extent of the cross-linking in the corneas was evaluated on the basis of fluorimetric analysis (excitation wave 365 nm, emission wave 450 nm) after collagen solubilization with papain.

FIG. 15 illustrates the fluorescence values for the formulations in this study, indicating the extent of cross-linking activity. Column A represents the fluorescence of the corneas treated with the 0.22% riboflavin solution with BAC. Column B represents the fluorescence of the corneas treated with the 0.22% riboflavin solution with the non-ionic agent. The results indicate that a smaller concentration of riboflavin passed through the 100 μm epithelium and the cross-linking is riboflavin-limited when the BAC formulation was employed. In general, epi-on cross-linking requires a sufficient riboflavin concentration in the stroma to achieve greater cross-linking efficiency.

Study 3

In a study, porcine eyes were treated according to the parameters indicated in FIG. 16. To provide a control, porcine eyes were soaked epi-off with 0.1% riboflavin solution for 20 minutes and then irradiated with continuous wave UVA light with an irradiance of 3 mW/cm² for a dose of 5.4 J/cm² while exposed to ambient air. To provide another control, porcine eyes were soaked epi-off with 0.22% riboflavin solution for 20 minutes and then irradiated with continuous wave UVA light with an irradiance of 30 mW/cm² for a dose of 7.2 J/cm² while exposed to ambient air. Additionally, porcine eyes were soaked epi-on with 0.22% riboflavin solution with BAC for 20 minutes and then irradiated with continuous wave UVA light with an irradiance of 30 mW/cm² for a dose of 7.2 J/cm² while exposed to ambient air. Porcine eyes were soaked epi-on with 0.22% riboflavin solution with a non-ionic agent for 20 minutes and then irradiated with continuous wave UVA light with an irradiance of 30 mW/cm² for a dose of 7.2 J/cm² while exposed to ambient air. Porcine eyes were soaked epi-on with 0.22% riboflavin solution with BAC for 20 minutes and then irradiated with pulsed UVA light with an irradiance of 30 mW/cm² for a dose of 7.2 J/cm² while exposed to 100% oxygen. Porcine eyes were soaked epi-on with 0.22% riboflavin solution with the non-ionic agent for 20 minutes and then irradiated with pulsed UVA light with an irradiance of 30 mW/cm² for a dose of 7.2 J/cm² while exposed to 100% oxygen.

The extent of the cross-linking in the corneas was evaluated on the basis of fluorimetric analysis. FIG. 17 shows the fluorescence values for the formulations in this study, indicating the extent of cross-linking activity. Columns A-F in FIG. 17 represent the results corresponding to the experimental parameters provided in respective rows A-F in FIG. 16. Columns C and D indicate that the cross-linking with the 0.22% riboflavin solution with BAC or the 0.22% riboflavin solution with the non-ionic agent was oxygen-limited. Columns E and F indicate that the cross-linking with the 0.22% riboflavin solution with BAC is riboflavin limited when compared to the cross-linking with the 0.22% riboflavin solution with the non-ionic agent. In addition, Columns E and F indicate that absorption by riboflavin in the saturated epithelium is not a significant factor when oxygen is applied.

In view of the foregoing, the diffusivity of riboflavin and the initial stromal concentration of riboflavin affects the extent of cross-linking activity. The results from the formulations including the non-ionic agent indicate that hydrophilic-lipophilic properties are a factor, allowing riboflavin to penetrate the epithelium and diffuse into the corneal hydrophilic stroma in quantities and duration appropriate for a clinical application.

Oxygen is a factor in efficient trans-epithelial (epi on) cross-linking. The results of the study show that the application of oxygen with the non-ionic agent provides cross-linking efficiencies similar to standard epi-off cross-linking.

Less oxygen may generally be available in the stroma due to the epithelial thickness as it relates to Fick's law of diffusion and due to photo-induced oxygen consumption in the epithelium. Thus, this study shows that the additional application of oxygen can enhance epi on cross-linking efficiency.

In addition, the absorption of UVA light by riboflavin-saturated epithelium may reduce photon efficiency. However, the results of this study indicate that, when oxygen is also applied, the absorption by riboflavin-saturated epithelium is not a predominate factor.

As described above, some riboflavin formulations include specific concentrations of Polidocanol to enhance permeability of the corneal epithelium. Advantageously, the concentrations of Polidocanol do not cause damage to the epithelium. Such riboflavin solutions may also include additives such as Fe(II).

Polidocanol and optionally additives can be employed in combination with other cross-linking techniques as described above to enhance delivery of riboflavin through the epithelium and achieve the desired amount of cross-linking activity. For instance, the riboflavin formulations with Polidocanol and optional additives can be applied with oxygen. Furthermore, the riboflavin solutions can be employed with different approaches for delivering photoactivating illumination (pulsed illumination, illumination of different patterns, etc.).

Study 4

To identify a new trans-epithelial formulation containing riboflavin, a study was conducted to test riboflavin formulations with Polidocanol as a less toxic and more efficient substitute for riboflavin formulation with benzalkonium chloride (BAC).

Pig eyes shipped overnight on ice from an abattoir (SiouxPreme, Sioux City, Iowa) were rinsed in saline. The eyes with intact epithelium were soaked with one of the test solutions below for 20 minutes in an incubator set at 37° C. by using a rubber ring to hold the solution on top.

For a Group A of the pig eyes, the following riboflavin formulations were used:

-   -   (a1) 0.25% riboflavin solution containing BAC (PARACEL™, Avedro,         Inc., Waltham, Mass.);     -   (a2) 0.1% w.v. riboflavin solution containing saline (PHOTREXA         ZD™, Avedro, Inc., Waltham, Mass.) with added riboflavin to         match the riboflavin content (0.25%) in solution (a1);     -   (a3) solution (a2) with 1% Polidocanol;     -   (a4) solution (a2) with 5% Polidocanol; and     -   (a5) solution (a2) with 10% Polidocanol.

The epitheliums of eyes in Group A were removed with a dull blade after the eyes were soaked in one of the solutions and irradiated pan-corneally on air with a top hat beam (3% root mean square) for 4 minutes with 365-nm light source (UV LED NCSU033B[T]; Nichia Co., Tokushima, Japan) at a chosen irradiance of 30 mW/cm² which was measured with a power sensor (model PD-300-UV; Ophir, Inc., Jerusalem, Israel) at the corneal surface. Corneal flaps (approximately 200 μm thick) were excised from the eyes with aid of an Intralase femtosecond laser (Abbot Medical Optics, Santa Ana, Calif.). The average thickness of the corneal flaps was calculated as a difference between the measurements before and after the excision from the eyes with an ultrasonic Pachymeter (DGH Technology, Exton, Pa.). The flaps were washed with distilled water and dried in a vacuum until the weight change became less than 10% (Rotary vane vacuum pump RV3 A652-01-903, BOC Edwards, West Sussex, UK). Each flap was digested for 2.5 h at 65° C. with 2.5 units/ml of papain (from Papaya latex, Sigma) in 1 ml of papain buffer [BBBS (pH 7.0-7.2), 2 mM L-cysteine and 2 mM EDTA]. Papain digests were diluted 0.5 times with 1×BBBS and fluorescence of the solutions was measured with excitation of 360 nm in a QM-40 Spectrofluorometer (Photon Technology Int., London, Ontario, Canada). The fluorescence of the papain buffer was taken into account by measuring fluorescence in the absence of tissue and subtracting this value from the fluorescence of the samples.

For a Group B of the pig eyes, the following riboflavin solutions were used:

-   -   (b1) 0.25% riboflavin solution containing BAC (PARACEL™);     -   (b2) 0.22% riboflavin solution containing saline (VIBEX XTRA™,         Avedro, Inc., Waltham, Mass.) with 1% Polidocanol;     -   (b3) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 5% Polidocanol; and     -   (b4) 0.22% riboflavin solution containing saline (VIBEX XTRA™).

The epitheliums of eyes in Group B were not removed after soaking in one of the solutions and the surfaces were briefly rinsed with a saline buffer before irradiation. The epitheliums were removed after the irradiation. Conditions used for the irradiation and the following treatment of the eyes were the same as for Group A.

For a Group C of the pig eyes, the following riboflavin solutions were used:

-   -   (c1) 0.25% riboflavin solution containing BAC (PARACEL™);     -   (c2) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 1% Polidocanol; and     -   (c3) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 3% Polidocanol.

The epitheliums of eyes in Group C were not removed after soaking in one of the solutions and the surfaces were briefly rinsed with a saline buffer before irradiation. The eyes were placed in a beaker with an oxygen stream for 2 minutes in the incubation chamber prior to irradiation. Corneas were pan-corneally irradiated with irradiance of 30 mW/cm², pulsed 1 sec on: 1 sec off for a total time of 8 min (7.2 J). The eyes were exposed to oxygen during all time of the treatment. The epithelium were removed from the cornea after the irradiation with a dull blade. Corneal flaps (approximately 200 μm thick) were excised from the eyes with aid of Intralase femtosecond laser and the following treatment of the flaps was the same as for the Groups A and B.

For a Group D and a Group E of the pig eyes, the following riboflavin solutions were used:

-   -   (d1) 0.25% riboflavin solution containing BAC (PARACEL™);     -   (d2) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 1% Polidocanol;     -   (d3) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 1% Polidocanol and 2.5 mM Fe(II).     -   (d4) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 3% Polidocanol; and     -   (d5) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 3% Polidocanol and 2.5 mM Fe(II).

For Group D, the experimental procedure (including the irradiation, oxygen exposure, and the cutting of the flaps) was the same as for Group C.

The epitheliums of eyes in Group E were removed after soaking in one of the solutions for 20 min. The eyes then were placed in a beaker with oxygen stream for 2 minutes in the incubation chamber prior to irradiation. Corneas were pan-corneally irradiated with irradiance of 30 mW/cm², pulsed 1 sec on: 1 sec off for total time of 8 min (7.2 J). The eyes were exposed to oxygen during all time of the treatment. Corneal flaps (approximately 200 μm thick) were excised from the eyes with aid of Intralase femtosecond laser and the following treatment of the flaps was the same as for the Groups A and B.

FIGS. 18-26 illustrate the cross-linking activity induced in Groups A-E by various riboflavin solutions. The cross-linking activity was measured as a ratio of fluorescence for the treated sample (F) to fluorescence for an untreated control (Fo), where emissions were recorded at a wavelength of 450 nm. Such measurement of cross-linking activity is described, for example, in U.S. Pat. No. 9,020,580, filed Jun. 4, 2012 and titled “Systems and Methods for Monitoring Time Based Photo Active Agent Delivery or Photo Active Marker Presence,” the contents of which are incorporated entirely herein by reference.

FIGS. 18 and 19 illustrate relative fluorescence for cross-linked corneal flaps treated with different surfactants in 0.22% riboflavin solution containing saline (VIBEX XTRA™) applied topically to pig eyes with intact epithelium for 20 min, after which the epithelium were then removed and the eyes were irradiated with 30 mW/cm² for 4 min. These results are presented in relation to corneal flaps treated with 0.25% riboflavin solution containing BAC (PARACEL™) under the same procedural conditions.

FIG. 20 illustrates relative fluorescence for cross-linked corneal flaps after using 1% solutions of different surfactants in 0.22% riboflavin solution containing saline (VIBEX XTRA™). These results are presented in relation to the fluorescence from corneal flaps treated with only 0.25% riboflavin solution containing BAC (PARACEL™) in the same procedural conditions. FIGS. 3-5 also show the HLB numbers for the surfactants, e.g., Polidocanol has an HLB number of 13.6.

For Group A, FIG. 21 illustrates relative fluorescence for cross-linked conical flaps treated with solution (a2) which does not include BAC relative to solution (a1) which includes BAC. Meanwhile, FIG. 22 illustrates relative fluorescence of cross-linked conical flaps treated with solutions (a3), (a4), and (a5) which include different concentrations of Polidocanol. These results are presented relative to conical flaps treated with solution (a1) which includes BAC and corneal flaps with no epithelium treated with solution (a2) which does not include Polidocanol or BAC.

For Group B, FIG. 23 illustrates relative fluorescence for cross-linked corneal flaps treated with solutions (b2) and (b3) which include 1% and 5% concentrations of Polidocanol respectively. These results are presented relative to corneal flaps treated with solution (b1) which includes BAC and corneal flaps treated with solution (b4) which does not include Polidocanol or BAC.

For Group C, FIG. 24 illustrates relative fluorescence of cross-linked conical flaps treated with solutions (c2) and (c3) which include 1% and 3% concentrations of Polidocanol respectively. These results are presented relative to conical flaps treated with solution (c1) which includes BAC.

FIG. 25 for Group D and FIG. 11 for Group E illustrate relative fluorescence of cross-linked flaps treated with solutions (d2) and (d4) which include 1% and 3% concentrations of Polidocanol respectively and with solutions (d3) and (d5) which include 2.5 mM iron(II) as well as 1% and 3% concentrations of Polidocanol respectively. These results are presented relative to conical flaps treated with solution (d1) which includes BAC. As described above, the epitheliums in Group D were not removed after soaking in the solutions, while the epitheliums in Group E were removed after soaking in the solutions.

As the results of the study show, the inventors have identified Polidocanol as a non-ionic surfactant that is more effective than many other surfactants for enhancing permeability and generating cross-linking activity. Although the use of BAC in riboflavin solutions may help riboflavin to pass through the epithelium, Polidocanol is far more effective and efficient than BAC in enhancing permeability in the epithelium and generating cross-linking activity. Advantageously, non-ionic agents, such as Polidocanol, are less corrosive and damaging to the epithelium than BAC.

Study 5

As described above, several permeability enhancers may be combined to achieve a specific HLB that achieves more optimal permeability for the epithelium. A study was conducted to test combinations of surfactants with different HLB numbers.

Intact epithelium were soaked for 20 min using one of the following solutions:

-   -   (e1) 0.25% riboflavin solution containing BAC (PARACEL™);     -   (e2) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 1% IGEPAL CO-630;     -   (e3) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 1% IGEPAL CO-720; and     -   (e4) 0.22% riboflavin solution containing saline (VIBEX XTRA™)         with 1% mixture of IGEPAL CO-630 with IGEPAL CO-720 (1:1 ratio).

The epitheliums of the eyes were removed and the eyes were irradiated with 30 mW/cm² for 4 min continuously on air. Corneal flaps with thickness of 200 μm were cut and the papain digestion and fluorescence analysis was conducted as previously described above.

FIG. 27 illustrates relative fluorescence of the cross-linked flaps treated with one of two different surfactants or a combination of the two surfactants. The cross-linking activity was measured as a ratio of fluorescence for the respective treated sample (F) to fluorescence for a sample treated with solution (e1) (Fparacel), where emissions were recorded at a wavelength of 450 nm.

The surfactant IGEPAL CO-630 has a HLB number of 13 and the surfactant IGEPAL CO-720 has a HLB number of 14, the 1:1 mixture has a HLB number of 13.5. As FIG. 12 shows, the mixture of the surfactants facilitates riboflavin permeation through the corneal epithelium more effectively than the surfactants employed individually.

Although the examples described herein may relate to the use of riboflavin and Polidocanol as a permeability enhancer for corneal cross-linking treatments, it is understood that other photosensitizers and/or other permeability enhancers (e.g., non-ionic surfactant with an appropriate HLB number) may be employed. Furthermore, other types of treatment are contemplated, such as antimicrobial photodynamic therapy, where enhanced or controlled delivery of a photosensitizer through an epithelium may be advantageous. Some microbes, such as fungi, have dormant phases, while other microbes, such as Acanthamoeba, can create cystic cell membrane barriers. Advantageously, additives that enhance permeability can increase penetration and uptake of photosensitizer by microbes/pathogens and enhance the antimicrobial effect of the photosensitizer. For instance, photosensitizer formulations employing a non-ionic permeability enhancer may be particularly effective for penetrating cysts, ulcers, etc. and treating microbes/pathogens. Other aspects of antimicrobial photodynamic therapy are described in U.S. patent application Ser. No. 15/137,748, filed Apr. 25, 2016 and titled “Systems and Methods for Photoactivating a Photosensitizer Applied to an Eye,” the contents of which is incorporated entirely herein by reference.

When riboflavin absorbs radiant energy, especially light, it undergoes photo activation. There are two photochemical kinetic pathways for riboflavin photoactivation, Type I and Type II. Some of the reactions involved in both the Type I and Type II mechanisms are as follows:

Common Reactions:

Rf→Rf ₁ *,I;  (r1)

Rf ₁ *→Rf,κ1;  (r2)

Rf ₁ *→Rf ₃*,κ2;  (r3)

Type I Reactions:

Rf ₃ *+DH→RfH ^(•) +D ^(•),κ3;  (r4)

2RfH ^(•) →Rf+RfH ₂,κ4;  (r5)

Type II Reactions:

Rf ₃*+O₂ →Rf+O₂ ¹,κ5;  (r6)

DH+O₂ ¹ →D _(ox),κ6;  (r7)

D _(ox) +DH→D−D,κ7;CXL  (r8)

In the reactions described herein, Rf represents riboflavin in the ground state. Rf*₁ represents riboflavin in the excited singlet state. Rf*₃ represents riboflavin in a triplet excited state. Rf^(•−) is the reduced radical anion form of riboflavin. RfH^(•) is the radical form of riboflavin. RfH₂ is the reduced form of riboflavin. DH is the substrate. DH^(•+) is the intermediate radical cation. D^(•) is the radical. D_(ox) is the oxidized form of the substrate.

Riboflavin is excited into its triplet excited state Rf*₃ as shown in reactions (r1) to (r3). From the triplet excited state Rf*₃, the riboflavin reacts further, generally according to Type I or Type II mechanisms. In the Type I mechanism, the substrate reacts with the excited state riboflavin to generate radicals or radical ions, respectively, by hydrogen atoms or electron transfer. In Type II mechanism, the excited state riboflavin reacts with oxygen to form singlet molecular oxygen. The singlet molecular oxygen then acts on tissue to produce additional cross-linked bonds.

Oxygen concentration in the cornea is modulated by UVA irradiance and temperature and quickly decreases at the beginning of UVA exposure. Utilizing pulsed light of a specific duty cycle, frequency, and irradiance, input from both Type I and Type II photochemical kinetic mechanisms can be employed to achieve a greater amount of photochemical efficiency. Moreover, utilizing pulsed light allows regulating the rate of reactions involving riboflavin. The rate of reactions may either be increased or decreased, as needed, by regulating, one of the parameters such as the irradiance, the dose, the on/off duty cycle, riboflavin concentration, soak time, and others. Moreover, additional ingredients that affect the reaction and cross-linking rates may be added to the cornea.

If UVA radiation is stopped shortly after oxygen depletion, oxygen concentrations start to increase (replenish). Excess oxygen may be detrimental in the conical cross-linking process because oxygen is able to inhibit free radical photopolymerization reactions by interacting with radical species to form chain-terminating peroxide molecules. The pulse rate, irradiance, dose, and other parameters can be adjusted to achieve a more optimal oxygen regeneration rate. Calculating and adjusting the oxygen regeneration rate is another example of adjusting the reaction parameters to achieve a desired amount of conical stiffening.

Oxygen content may be depleted throughout the cornea, by various chemical reactions, except for the very thin corneal layer where oxygen diffusion is able to keep up with the kinetics of the reactions. This diffusion-controlled zone will gradually move deeper into the cornea as the reaction ability of the substrate to uptake oxygen decreases.

Riboflavin is reduced (deactivated) reversibly or irreversibly and/or photo-degraded to a greater extent as irradiance increases. Photon optimization can be achieved by allowing reduced riboflavin to return to ground state riboflavin in Type I reactions. The rate of return of reduced riboflavin to ground state in Type I reactions is determined by a number of factors. These factors include, but are not limited to, on/off duty cycle of pulsed light treatment, pulse rate frequency, irradiance, and dose. Moreover, the riboflavin concentration, soak time, and addition of other agents, including oxidizers, affect the rate of oxygen uptake. These and other parameters, including duty cycle, pulse rate frequency, irradiance, and dose can be selected to achieve more optimal photon efficiency and make efficient use of both Type I as well as Type II photochemical kinetic mechanisms for riboflavin photosensitization. Moreover, these parameters can be selected in such a way as to achieve a more optimal chemical amplification effect.

In addition to the photochemical kinetic reactions (r1)-(r8) above, however, the present inventors have identified the following photochemical kinetic reactions (r9)-(r26) that also occur during riboflavin photoactivation:

Additional:

Aggregation:

Peroxides:

2O₂ ⁻→O₂+H₂O₂,κ₁₂  (r25)

OH^(∘) +CXL→inert products,κ_(OH)  (r26)

FIG. 2A illustrates a diagram for the photochemical kinetic reactions provided in reactions (r1) through (r26) above. The diagram summarizes photochemical transformations of riboflavin (Rf) under UVA photoactivating light and its interactions with various donors (DH) via electron transfer. As shown, cross-linking activity occurs: (A) through the presence of singlet oxygen in reactions (r6) through (r8) (Type II mechanism); (B) without using oxygen in reactions (r4) and (r17) (Type I mechanism); and (C) through the presence of peroxide (H₂O₂), superoxide (O₂ ⁻), and hydroxyl radicals (.OH) in reactions (r13) through (r17).

As shown in FIG. 2A, the present inventors have also determined that the cross-linking activity is generated to a greater degree from reactions involving peroxide, superoxide, and hydroxyl radicals. Cross-linking activity is generated to a lesser degree from reactions involving singlet oxygen and from non-oxygen reactions. Some models based on the reactions (r1)-(r26) may account for the level of cross-linking activity generated by the respective reactions. For instance, where singlet oxygen plays a smaller role in generating cross-linking activity, models may be simplified by treating the cross-linking activity resulting from singlet oxygen as a constant.

All the reactions start from Rf₃* as provided in reactions (r1)-(r3). The quenching of Rf₃* occurs through chemical reaction with ground state Rf in reaction (r10), and through deactivation by the interaction with water in reaction (r9).

As described above, excess oxygen may be detrimental in corneal cross-linking process. As shown in FIG. 2A, when the system becomes photon-limited and oxygen-abundant, cross-links can be broken from further reactions involving superoxide, peroxide, and hydroxyl radicals. Indeed, in some cases, excess oxygen may result in net destruction of cross-links versus generation of cross-links.

As described above, a large variety of factors affect the rate of the cross-linking reaction and the amount of biomechanical stiffness achieved due to cross-linking. A number of these factors are interrelated, such that changing one factor may have an unexpected effect on another factor. However, a more comprehensive model for understanding the relationship between different factors for cross-linking treatment is provided by the photochemical kinetic reactions (r1)-(r26) identified above. Accordingly, systems and methods can adjust various parameters for cross-linking treatment according to this photochemical kinetic cross-linking model, which provides a unified description of oxygen dynamics and cross-linking activity. The model can be employed to evaluate expected outcomes based on different combinations of treatment parameters and to identify the combination of treatment parameters that provides the desired result. The parameters, for example, may include, but is not limited to: the concentration(s) and/or soak times of the applied cross-linking agent; the dose(s), wavelength(s), irradiance(s), duration(s), and/or on/off duty cycle(s) of the photoactivating light; the oxygenation conditions in the tissue; and/or presence of additional agents and solutions.

A model based on the reactions (r1)-(r19) has been validated by at least six different methods of evaluating cross-linking activity:

-   -   Extensiometry experiments     -   Oxygen depletion experiments     -   Non-linear optical microscopy fluorescence experiments     -   Fluorescence data based on papain digestion method experiments     -   Brillouin microscopy experiments     -   Corneal stromal demarcation line correlation experiments

For extensiometry experiments, corneas were soaked with riboflavin for 20 minutes and exposed to UVA photoactivating light in ambient air at an irradiance of 3 mW/cm² for 7.5 minutes (dose of 1.35 J/cm²), 15 minutes (dose of 2.70 J/cm²), 30 minutes (dose of 5.4 J/cm²), 45 minutes (dose of 8.10 J/cm²), 120 minutes (dose of 21.6 J/cm²), and 150 minutes (dose of 27.0 J/cm²). Extensiometry measurements were taken for 200 μm flaps of the corneas. FIG. 31 illustrates a graph of cross-link profiles (cross-link concentration as a function of corneal depth) calculated by the model for each cross-linking treatment. FIG. 32 illustrates a correlation between the extensiometry measurements and the values calculated by the model (area under the curve for 200 μm). In general, there is a good correlation between the biomechanics determined in the extensiometry experiments and the values calculated by the model. It can also be seen from FIG. 31 that cross-linking can saturate when particular treatment parameters (e.g., longer irradiation times) are employed.

For the oxygen depletion experiments, O₂ concentrations were measured and calculated at a depth of approximately 100 μm to approximately 200 μm for corneas treated with riboflavin. FIG. 3A illustrates a graph of data showing the correlation between the theoretical values based on the model and experimental data for corneas exposed to continuous wave UVA photoactivating light at an irradiance of 3 mW/cm². FIGS. 3B-C illustrate graphs of data showing the correlation between model values and experimental data for corneas exposed to long term pulses and short term pulses, respectively, at an irradiance of 3 mW/cm².

For the non-linear optical microscopy fluorescence experiments, the cross-linking profiles based on corneal depth were determined for corneas treated with riboflavin and exposed to UVA photoactivating light at an irradiance of 3 mW/cm². FIG. 4 illustrates a graph of data showing the correlation between model and experimental data for corneas exposed for 15 minutes and 30 minutes. The third party experimental data was published in Dongyul Chai et al. “Quantitative Assessment of UVA-riboflavin Corneal Cross-Linking Using Nonlinear Optical Microscopy.” Investigative Ophthalmology & Visual Science. June 2011, Vol. 52, No. 7, pp. 4231-4238, the contents of which are incorporated entirely herein by reference.

For the fluorescence data based on papain digestion method experiments, cross-linking concentrations were evaluated based on fluorescent light intensity. FIG. 5A illustrates a graph of data showing the correlation of model values and experimental data for corneal flaps (taken from 0 to approximately 100 μm deep) exposed to combinations of riboflavin concentrations (0.1%, 0.25%, and 0.5%) and 5.4 J/cm² doses of UVA photoactivating light at irradiances of 3 mW/cm² and 30 mW/cm² for 3 minutes and 30 minutes. Similarly, FIG. 5B illustrates a graph of data showing the correlation of model values and experimental data for corneal flaps (taken from approximately 100 μm to approximately 200 μm deep) exposed to combinations of riboflavin concentrations (0.1%, 0.25%, and 0.5%) and 5.4 J/cm² doses of UVA photoactivating light at irradiances of 3 mW/cm² and 30 mW/cm² for 3 minutes and 30 minutes. FIG. 5C illustrates a graph of data showing the correlation of model values and experimental data for corneal flaps treated with a concentration of riboflavin and exposed to full oxygen concentration and 5.4 J/cm² and 7.2 J/cm² doses of continuous wave UVA photoactivating light at irradiances of 3 mW/cm², 10 mW/cm², 15 mW/cm², 30 mW/cm², 45 mW/cm², 60 mW/cm², and 100 mW/cm².

FIG. 5D illustrates a graph of data showing the correlation of model values and experimental data for corneal flaps (taken from approximately 0 μm to approximately 200 μm deep) treated with a concentration of 0.1% riboflavin and exposed to air or full oxygen concentration and a 5.4 J/cm² doses of continuous wave UVA photoactivating light at irradiances of 3 mW/cm², 10 mW/cm², 15 mW/cm², 30 mW/cm², 45 mW/cm², 60 mW/cm², and 100 mW/cm². The values at irradiance 3 mW/cm² under 100% oxygen shows the effect of quenching Rf₃* by oxygen.

Brillouin microscopy experiments are described in Scarcelli G et al., Invest. Ophthalmol. Vis. Sci. (2013), 54: 1418-1425, the contents of which are incorporated entirely herein by reference. The experiments measured Brillouin modulus values quantifying corneal mechanical properties after various cross-linking treatments. FIG. 28A shows Brillouin modulus values measured at anterior, central, and posterior sections of corneas experimentally soaked in riboflavin for various durations and irradiated with UV light for various durations. FIG. 28B illustrates the correlation between the experimentally measured values and values calculated with the model for various treatments. Treatment A in FIG. 28B corresponds to a soak time of 30 minutes and irradiation of 5 minutes. Treatment B corresponds to a soak time of 30 minutes and irradiation of 15 minutes. Treatment C corresponds to a soak time of 30 minutes and irradiation of 30 minutes. Treatment D corresponds to a soak time of 30 minutes and irradiation of 5 minutes. Treatment E corresponds to a soak time of 5 minutes and irradiation of 30 minutes. Treatment E corresponds to a soak time of 30 minutes and irradiation of 30 minutes.

For the corneal stromal demarcation correlation experiments, corneal stromal demarcation lines were evaluated for treated corneas. A method for these experiments involves slit-lamp examination (slit projection and Scheimpflug camera). See Theo Seiler and Farhad Hafezi, “Corneal Cross-Linking-Induced Stromal Demarcation Line,” Cornea, October 2006; 25:1057-59, the contents of which are incorporated entirely herein by reference. Another method involves corneal optical coherence tomography (OCT). See Luigi Fontana, Antonello Moramarco, “Esperienze personali con CXL accelerate,” UOC Oculistica ASMN-IRCCS Reggio Emilia. Roma, 20 settembre 2014, the contents of which are incorporated entirely herein by reference. A further method involves confocal microscopy. See C. Mazzotta et al., “Treatment of Progressive Keratoconus by of Corneal Collagen In Vivo Confocal Microscopy in Humans,” Cornea, vol. 26, no. 4, May 2007, the contents of which are incorporated entirely herein by reference.

Corneal stromal healing involves the deposition of new collagen, which produces haze and scattering. Slit-lamp examination and OCT can detect this hyper-reflectivity and possibly a significant change in the spatial order factor (change in birefringence, i.e., index variation). Corneal stromal demarcation lines indicate the threshold at which the healing response occurs. This conclusion is corroborated by confocal microscopy. The demarcation lines can also be seen as a transition zone between cross-linked anterior corneal stroma and untreated posterior corneal stroma.

The six evaluations described above show a strong correlation between the experimental data and the calculations generated by a model based on the photochemical kinetic reactions identified above. The model is extremely effective and accurate in predicting the results of riboflavin cross-linking treatments applied according to various combinations of parameters. Accordingly, using such a model, systems and methods can more efficiently and predictably achieve a desired profile of cross-linking activity throughout the cornea. The model allows the systems and methods to identify a more optimal combination of parameters for cross-linking treatment. Therefore, the model can be used to determine the set up for different aspects of cross-linking treatment systems as described above.

As shown in FIG. 2B, aspects of the system of reactions can be affected by different parameters. For instance, the irradiance at which photoactivating light is delivered to the system affects the photons available in the system to generate Rf₃* for subsequent reactions. Additionally, delivering greater oxygen into the system drives the oxygen-based reactions. Meanwhile, pulsing the photoactivating light affects the ability of the reduced riboflavin to return to ground state riboflavin by allowing additional time for oxygen diffusion. Of course, other parameters can be varied to control the system of reactions.

A model based on the photochemical kinetic reactions (r1)-(r26) can generate cross-link profiles for treatments using different protocols as shown in FIGS. 7A-C. In particular, each protocol determines the dose of the photoactivating UVA light, the irradiance for the UVA photoactivating light, the treatment time, and the concentration of oxygen delivered to the corneal surface. The cornea has been treated with a formulation including 0.1% concentration riboflavin. FIG. 7A illustrates cross-link profiles for treatments that deliver a dose of 7.2 J/cm² of UVA light under normal (ambient) oxygen according to different irradiances and different treatment times. FIG. 7B illustrates cross-link profiles for treatments that employ different irradiances of continuous or modulated (pulsed) UVA light and different treatment times under normal or 100% oxygen concentration. FIG. 7C illustrates cross-link profiles for treatments that deliver an irradiance of 3 mW of UVA light for 30 minutes with different oxygen conditions (normal, 100%, or 0.01×) at the corneal surface.

The cross-link profiles in FIGS. 7A-C provide the cross-link concentration as a function of corneal depth. In general, the three-dimensional distribution of cross-links in the cornea as indicated by each cross-link profile depends on the combination of different treatment parameters. Protocols employing different sets of treatment parameters can be provided as input into the model and the model can output the resulting three-dimensional distribution of cross-links in the cornea. Accordingly, the model can be used to select treatment parameters to achieve the desired distribution of cross-links in the cornea.

FIG. 6A illustrates a graph of data showing the correlation of model values and experimental data for the depths of corneal stromal demarcation lines for the protocols described in FIG. 6B.

As described above, corneal stromal demarcation lines indicate the transition zone between cross-linked anterior corneal stroma and untreated posterior corneal stroma. As also shown in FIG. 8A-C, cross-link profiles generated by the model can be evaluated to determine the depth at which the demarcation line may appear at a cross-link concentration of approximately 5 mol/m³. Here, the demarcation line may be understood as the threshold at which a healing response occurs in response to the distribution of cross-links as well as the effect of reactive oxygen species on the corneal tissue. The cornea has been treated with a formulation including 0.1% concentration riboflavin. FIG. 8A illustrates a cross-link profile for a treatment that delivers a dose of 5.4 J/cm² of photoactivating UVA light under normal oxygen according to an irradiance of 3 mW/cm² and a treatment time of 30 minutes. FIG. 8A shows that a cross-link concentration of approximately 5 mol/m³ (demarcation line) occurs at a depth of approximately 290 μm in the resulting cross-link profile. FIG. 8B illustrates cross-link profiles for treatments that deliver different doses of photoactivating UVA light according to different irradiances and different treatment times under normal oxygen. FIG. 8C illustrates cross-link profiles for treatments that deliver different doses of photoactivating UVA light according to different irradiances and different treatment times under normal or 100% oxygen concentration.

FIGS. 8B-C shows that the depths for the demarcation line vary with the different cross-link profiles generated by the different sets of treatment parameters. The depths of the demarcation line indicated by the different cross-link profiles may be employed to select treatment parameters. For instance, treatment parameters may be selected to ensure that the cross-links do not occur at a depth where undesired damage may result to the endothelium. This analysis allows the treatment system to accommodate different corneal thicknesses, particularly thin corneas.

Correspondingly, FIGS. 9A-B illustrate graphs of demarcation depth (cross-link concentration of approximately 5 mol/m³) as a function of dose of UVA photoactivating light. The determination of the demarcation depths are based on cross-link profiles generated by the model for treatments using different protocols. The cornea has been treated with a formulation including 0.1% concentration riboflavin. FIG. 9A illustrates graphs for treatments that deliver continuous or pulsed UVA photoactivating light according to different irradiances under normal oxygen. FIG. 9B illustrates graphs for treatments that deliver continuous or pulsed UVA photoactivating light according to different irradiances under a greater concentration of oxygen.

FIG. 10 illustrates the cross-link profiles for treatments employing different protocols as generated by the model. FIG. 10 also shows a demarcation line that corresponds to biomechanical stiffness threshold at a cross-link concentration of 10 mol/m³. The demarcation line intersects the cross-link profiles at varying depths (biomechanical stiffness depth) based on the different treatment parameters of the protocols. FIG. 11 illustrates the measurement of maximum keratometry (K_(max)) (diopters) at three, six, and twelve months relative to a baseline for corneas that were experimentally treated according to the protocols employed for FIG. 10.

FIGS. 12A-B illustrate the correlation between the experimental data of FIG. 11 and the cross-link profiles generated for FIG. 10 by the model. For the biomechanical stiffness depth determined for each protocol in FIG. 10, FIG. 12A plots the experimental change of K_(max) for months six and twelve corresponding to the respective protocol. FIG. 12A also shows a quadratic fit of the plotted data for each month six and twelve. The quadratic fit is consistent with the quadratic nature of shear forces (in the x-y plane) resulting from a force placed on a disk (along the z-axis) according to thin shell theory.

Meanwhile, for the area above the demarcation line for the cross-link profile for each protocol in FIG. 10, FIG. 12B plots the experimental change of K_(max) for months six and twelve corresponding to the respective protocol. FIG. 12B also shows a linear fit of the plotted data for each month six and twelve.

The quadratic fit for the two curves in FIG. 12A are substantially similar. Similarly, the linear fit for the two curves in FIG. 12B are substantially similar. The correlations shown in FIGS. 12A-B indicate that there is a predictable biomechanical/healing response over time for a given set of treatment parameters. In view of the verification of the experimental data points, the model, as well as thin shell analysis, one can predictably determine refractive change according to the radius and depth of the disk corresponding to the myopic correction. In general, the distribution of cross-links effects refractive change. By accurately determining the distribution of cross-links, the model can be employed to determine this refractive change.

FIG. 29 illustrates concentration of cross-link concentration as well as a function of corneal depth with a demarcation depth of approximately 360 μm. FIG. 29 also shows a line of demarcation analysis using a second derivative and threshold algorithm. The second derivative can also be calculated as shown. At the illustrated demarcation depth, the second derivative has a threshold derivative of 180 mM/mm².

FIGS. 35-36 illustrate graphs of cross-link profiles for treatments employing different protocols, as generated by the model. The graphs also show a potential threshold cross-link concentration of approximately 4.4 mM/m³ for the demarcation line. As shown, the demarcation depth is taken at a shift of approximately 125 μm from the intersection of the cross-link profile curve and the potential threshold cross-link concentration. In FIG. 35, for instance, the demarcation line occurs at a depth of approximately 350 μm.

The model of photochemical kinetic reactions was further evaluated against the results reported by fourteen different studies in total. FIG. 30 illustrates a graph of data showing the correlation of model values and experimental data for the depths of corneal stromal demarcation lines for protocols described in these fourteen separate studies. The measurements are taken from the epithelial surface. The standard deviation is approximately 20 μm.

TABLE 1 shows further shows data for determination of demarcation line depth for different treatments.

TABLE 2 Demarcation line depth Conventional CXL C-light ACXL P-light ACXL TE CXL TE ACXL CXL Treatments 44 eyes 10 eyes 10 eyes 10 eyes 10 eyes 84 eyes 3 mW 30 mW 30 mW 3 mW 45 mW Average demarcation 350 ± 20 μm 200 ± 20 μm 250 ± 20 μm 100 ± 20 μm 100 ± 20 μm line depth (measured from epithelial surface) *Average epithelial thickness: 50 ± 10 μm. CXL, conventional crosslinking: C-light ACXL, continous light accelerated crosslinking: P-light ACXL, pulsed light accelerated crosslinking; TE CXL, transepithelial crosslinking; TE ACXL, transepithelial accelerated crosslinking.

The reported standard deviations reveal variability in the depth of the demarcation line for nominally equivalent clinical protocols. Such variability may be the result of aspects of measurement error, clinical technique, protocol, the riboflavin formulation, and/or the equipment employed. An analysis of the reported variability was performed with the model of photochemical kinetic reactions. FIG. 37 illustrates that the demarcation line depth may be affected by aspects of the riboflavin concentration, the use of thickening agent, irradiation (UVA) device calibration, irradiation (UVA) beam profile, and/or geographic factors.

In sum, the line of demarcation is predicted accurately the model of photochemical kinetic reactions. As such, the model of photochemical kinetic reactions may be used to treat corneas, particularly thinner corneas, more safely. However, changes in clinical protocol may result in variability in the depth of the line of demarcation line and potentially clinical outcomes, suggesting the importance of precision in cross-linking treatment methodology. Consistency in protocol, technique and equipment can enhance the predictability of the clinical outcomes.

According to an embodiment, FIG. 13 illustrates the example system 100 employing a model based on the photochemical kinetic reactions (r1)-(r26) identified above to determine an amount of cross-linking that results from treatment parameters and/or other related information. The controller 120 includes a processor 122 and computer-readable storage media 124. The storage media 124 stores program instructions for determining an amount of cross-linking when the photoactivating light from the light source 110 is delivered to a selected region of a cornea treated with a cross-linking agent. In particular, a photochemical kinetic model 126 based on the reactions (r1)-(r26) may include a first set of program instructions A for determining cross-linking resulting from reactions involving reactive oxygen species (ROS) including combinations of peroxides, superoxides, hydroxyl radicals, and/or singlet oxygen and a second set of program instructions B for determining cross-linking from reactions not involving oxygen. The controller 120 receives input relating to treatment parameters and/or other related information. The controller 120 can then execute the program instructions A and B to output information relating to three-dimensional cross-link distribution(s) for the selected region of the cornea based on the input. The three-dimensional cross-link distribution(s) may then be employed to determine how to control aspects of the light source 110, the optical elements 112, the cross-linking agent 130, the applicator 132, the oxygen source 140, and/or oxygen delivery device 142 in order to achieve a desired treatment in selected region of the cornea. (Of course, the system 100 shown in FIG. 13 and this process can be used for treatment of more than one selected region of the same cornea.)

According to one implementation, the three-dimensional cross-link distribution(s) may be evaluated to calculate a threshold depth corresponding to a healing response due to the cross-links and an effect of the reactive-oxygen species in the selected region of the cornea. Additionally or alternatively, the three-dimensional cross-link distribution(s) may be evaluated to calculate a biomechanical tissue stiffness threshold depth corresponding to a biomechanical tissue response in the selected region of the cornea. The information on the depth of the healing response and/or the biomechanical tissue stiffness in the cornea can be employed to determine how to control aspects of the light source 110, the optical elements 112, the cross-linking agent 130, the applicator 132, the oxygen source 140, and/or oxygen delivery device 142. Certain healing response and/or biomechanical tissue stiffness may be desired or not desired at certain depths of the cornea.

Referring to FIG. 33, the photochemical kinetic model allows particular aspects of the photochemical process to be controlled or otherwise influenced to produce desired cross-linking activity. For instance, different additives, such as iron, may be employed to affect mechanisms at different points of the photochemical process as shown in FIG. 33. FIG. 34 shows the effect of the various additives in FIG. 33 on cross-linking activity.

According to another embodiment, FIG. 38 illustrates the example system 100 employing the photochemical kinetic model 126 to determine treatment parameters for achieving desired biomechanical changes in the cornea, e.g., a refractive correction. As in FIG. 13, the controller 120 includes the processor 122 and the computer-readable storage media 124. In the example of FIG. 14, however, the storage media 124 stores program instructions 125 for determining what treatment parameters may be employed to achieve desired biomechanical changes. The program instructions 125 are based on the photochemical kinetic model 126 which employ the reactions (r1)-(r26) to determine cross-linking resulting from (i) reactions involving reactive oxygen species (ROS) including combinations of peroxides, superoxides, hydroxyl radicals, and/or singlet oxygen and (ii) reactions not involving oxygen.

Using the photochemical kinetic model 126, a three-dimensional distribution of resulting cross-links throughout the treated corneal tissue can be determined for a combination of treatment parameters. As described above, parameters for cross-linking treatment may include: the concentration(s) and/or soak times of the applied cross-linking agent; the dose(s), wavelength(s), irradiance(s), duration(s), on/off duty cycle(s), and/or other illumination parameters for the photoactivating light; the oxygenation conditions in the tissue; and/or presence of additional agents and solutions. The resulting distribution of cross-links determined from the photochemical kinetic model 126 can be correlated to a particular biomechanical change in the cornea. FIGS. 12A-B show, for instance, the correlation between the distribution of cross-links and refractive change.

As shown in FIG. 38, the controller 120 receives an input 12 relating to the initial biomechanical state of the cornea and an input 14 indicating a desired biomechanical change for the cornea, e.g., for refractive correction. The initial biomechanical state, for instance, can be determined according to approaches described in U.S. Patent Application Publication No. 2012/0215155 referenced above. In some cases, the input 12 may be provided by a measurement system communicatively coupled to the controller 120. It is understood that the initial biomechanical state may reflect the state of the cornea prior to any treatment or during a treatment.

The inputs 12, 14 may be expressed in terms of corneal topography (i.e., shape), corneal strength (i.e., stiffness), and/or corneal thickness. For instance, the desired biomechanical change for refractive correction may be determined from a correction specified (by a practitioner) in diopters, e.g., “a 1.5 diopter correction.”

A desired biomechanical change in the cornea can be correlated to a particular distribution of cross-links as determined by the photochemical kinetic model 126. As such, the controller 120 can execute the program instructions 125 to determine the particular distribution of cross-links 16 that can generate the desired biomechanical change specified by the input 14 in a cornea having the initial biomechanical state specified by the input 12. After determining the distribution of cross-links 16 for the desired biomechanical change, the controller 120 can prescribe a set of treatment parameters for achieving the specified distribution of cross-links.

As the studies above establish, however, the distribution of cross-links 16 might be achieved in many cases by more than one set of treatment parameters. For instance, depending on the photochemical kinetic reactions, similar distributions of cross-links may be achieved by applying: (i) a lower dose of photoactivating light for a longer amount of time, or (ii) a higher dose of photoactivating light for a shorter amount of time. Therefore, more than one set of treatment parameters 18 for achieving the distribution of cross-links 16 may be identified.

With more than one possible set of treatment parameters 18, a practitioner can optimize the treatment for certain preferred parameters, such as treatment time or dose of photoactivating light. For instance, the practitioner may optimize the treatment parameters to achieve shorter treatment times. For this preference, the controller 120 may prescribe a set of illumination parameters that provide a larger dose of photoactivating light that yields the distribution of cross-links 16 over shorter illumination durations. Conversely, the practitioner may optimize the treatment parameters to employ smaller doses of photoactivating light. For this second preference, the controller 120 may prescribe a set of illumination parameters that provide a smaller dose of photoactivating light that yields the distribution of cross-links 16 over longer illumination durations.

In general, to achieve the distribution of cross-links 16, the controller 120 may identify any of the different combinations 18 of values for a set of treatment parameters A, B, C, D, E, etc., as described above. The practitioner can set preferences for one or more of these treatment parameters. For instance, the practitioner may initially set a preferred value or range of preferred values for parameter A. In response, the controller 120 can specify combinations of values for the remaining parameters B, C, D, E, etc., that meet the preference for parameter A while achieving the distribution of cross-links 16. The practitioner may make selections for the values of the parameters B, C, D, and/or E, etc., based on further preferences to arrive at an optimized set of treatment parameters 18 a. The process of optimizing the treatment parameters may be iterative as the values for the treatment parameters are incrementally tuned to meet preferences having varying priorities.

In some embodiments, the practitioner may manage the optimization process through a series of selections and other inputs via a user interface (not shown) coupled to the controller 120. In some cases, the inputs 12, 14 may also be provided through such a user interface.

The final set of treatment parameters 18 a can then be employed to determine how to control aspects of the light source 110, the optical elements 112, the cross-linking agent 130, the applicator 132, the oxygen source 140, oxygen delivery device 142, etc., in order to achieve a desired treatment in selected region of the cornea.

Correspondingly, FIG. 39 illustrates an example method 200 for employing a model of photochemical kinetic reactions (r1)-(r26) to determine treatment parameters for achieving desired biomechanical changes. In step 202, information relating to the initial biomechanical state of a cornea is received. In step 204, information relating to a desired biomechanical change for the cornea, e.g., for refractive correction, is received. In step 206, a distribution of cross-links is determined to achieve the desired biomechanical change in a cornea having the initial biomechanical state. In step 208, one or more sets of treatment parameters are determined to achieve the distribution of cross-links. In association with step 208, one or more preferences for treatment parameters may be received in step 210, and the treatment parameters may be optimized in step 212 based on the one or more preferences to determine a final set of treatment parameters that can be implemented in a treatment system (e.g., the example system 100) to achieve the distribution of cross-links.

As described above, according to some aspects of the present disclosure, some or all of the steps of the above-described and illustrated procedures can be automated or guided under the control of a controller (e.g., the controller 120). Generally, the controllers may be implemented as a combination of hardware and software elements. The hardware aspects may include combinations of operatively coupled hardware components including microprocessors, logical circuitry, communication/networking ports, digital filters, memory, or logical circuitry. The controller may be adapted to perform operations specified by a computer-executable code, which may be stored on a computer readable medium.

As described above, the controller may be a programmable processing device, such as an external conventional computer or an on-board field programmable gate array (FPGA) or digital signal processor (DSP), that executes software, or stored instructions. In general, physical processors and/or machines employed by embodiments of the present disclosure for any processing or evaluation may include one or more networked or non-networked general purpose computer systems, microprocessors, field programmable gate arrays (FPGA's), digital signal processors (DSP's), micro-controllers, and the like, programmed according to the teachings of the example embodiments of the present disclosure, as is appreciated by those skilled in the computer and software arts. The physical processors and/or machines may be externally networked with the image capture device(s), or may be integrated to reside within the image capture device. Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the example embodiments, as is appreciated by those skilled in the software art. In addition, the devices and subsystems of the example embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as is appreciated by those skilled in the electrical art(s). Thus, the example embodiments are not limited to any specific combination of hardware circuitry and/or software.

Stored on any one or on a combination of computer readable media, the example embodiments of the present disclosure may include software for controlling the devices and subsystems of the example embodiments, for driving the devices and subsystems of the example embodiments, for enabling the devices and subsystems of the example embodiments to interact with a human user, and the like. Such software can include, but is not limited to, device drivers, firmware, operating systems, development tools, applications software, and the like. Such computer readable media further can include the computer program product of an embodiment of the present disclosure for performing all or a portion (if processing is distributed) of the processing performed in implementations. Computer code devices of the example embodiments of the present disclosure can include any suitable interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes and applets, complete executable programs, and the like. Moreover, parts of the processing of the example embodiments of the present disclosure can be distributed for better performance, reliability, cost, and the like.

Common forms of computer-readable media may include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other suitable magnetic medium, a CD-ROM, CDRW, DVD, any other suitable optical medium, punch cards, paper tape, optical mark sheets, any other suitable physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read.

While the present disclosure has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present disclosure. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the invention. It is also contemplated that additional embodiments according to aspects of the present disclosure may combine any number of features from any of the embodiments described herein. 

What is claimed is:
 1. A formulation for an eye treatment, comprising: a photosensitizer; and a permeability enhancing composition including one or more permeability enhancers, the permeability enhancing composition having a Hydrophile-Lipophile Balance (HLB) number indicating that the permeability enhancing composition increases a permeability of an area of the eye for the photosensitizer.
 2. The formulation of claim 1, wherein the permeability enhancing composition includes a plurality of permeability enhancers, the HLB number for the permeability enhancing composition being equal to a sum of products multiplying a percentage of each permeability enhancer in the permeability enhancing composition and a HLB number for the respective permeability enhancer.
 3. The formulation of claim 1, further comprising at least one additive selected from the group consisting of iron, copper, manganese, chromium, vanadium, aluminum, cobalt, mercury, cadmium, nickel, arsenic, 2,3-butanedione, and folic acid.
 4. The formulation of claim 3, wherein the at least one additive includes iron(II).
 5. The formulation of claim 1, wherein the area of the eye is a corneal epithelium.
 6. The formulation of claim 5, wherein the photosensitizer includes riboflavin and the permeability enhancing composition has a HLB number between approximately 12.6 and approximately 14.6.
 7. The formulation of claim 1, wherein the area of the eye is an area infected by a pathogen.
 8. A method for treating an eye, comprising: applying a formulation to an area of an eye, the formulation including: a photosensitizer; and permeability enhancing composition including one or more permeability enhancers, the permeability enhancing composition having a Hydrophile-Lipophile Balance (HLB) number indicating that the permeability enhancing composition increases a permeability of an area of the eye for the photosensitizer; and photoactivating the photosensitizer by delivering a dose of illumination to the area of the eye.
 9. The method of claim 8, wherein the permeability enhancing composition includes a plurality of permeability enhancers, and the HLB number for the permeability enhancing composition being equal to a sum of products multiplying a percentage of each permeability enhancer in the permeability enhancing composition and a HLB number for the respective permeability enhancer.
 10. The method of claim 8, wherein the formulation further includes at least one additive selected from the group consisting of iron, copper, manganese, chromium, vanadium, aluminum, cobalt, mercury, cadmium, nickel, arsenic, 2,3-butanedione, and folic acid.
 11. The method of claim 10, wherein the at least one additive includes iron (II).
 12. The method of claim 8, further comprising applying a concentration of oxygen to the cornea.
 13. The method of claim 8, wherein applying the formulation includes applying the formulation to an area of the eye infected by a pathogen, whereby photoactivation of the photosensitizer provides an antimicrobial effect on the area infected by the pathogen.
 14. The method of claim 8, wherein applying the formulation includes applying the formulation to a corneal epithelium.
 15. The method of claim 14, wherein the photosensitizer includes riboflavin, the permeability enhancing composition has a HLB number between approximately 12.6 and approximately 14.6, and the illumination includes ultraviolet light.
 16. A formulation for a corneal treatment, comprising: a photosensitizer; and a non-ionic surfactant including a molecule having a hydrophilic and lipophilic balance that increases the permeability of the corneal epithelium for the photosensitizer.
 17. The formulation of claim 16, wherein the photosensitizer includes riboflavin and the non-ionic surfactant has a Hydrophile-Lipophile Balance (HLB) number between approximately 12.6 and approximately 14.6.
 18. The formulation of claim 17, wherein the non-ionic surfactant includes Polyoxyethylene (9) lauryl ether.
 19. The formulation of claim 16, further comprising at least one additive including selected from the group consisting of iron, copper, manganese, chromium, vanadium, aluminum, cobalt, mercury, cadmium, nickel, arsenic, 2,3-butanedione, and folic acid.
 20. The formulation of claim 19, wherein the at least one additive includes iron(II). 